This invention relates generally to solid state radiation imagers, and more particularly to depositing scintillator material on x-ray detector arrays.
Solid state radiation imaging devices typically include an array of photosensors coupled to a scintillator. Radiation incident on the scintillator is absorbed, resulting in the generation of optical photons which, in turn, are detected by the photosensor array to generate a corresponding electrical signal. A key factor in imager performance relates to the effective disposition and coupling of the scintillator to the photosensor array.
A typical scintillator material in radiation imaging arrays is Cesium Iodide (CsI). The cesium iodide is disposed over the detector array the active portion of the detector array, that is, the area in which incident X-ray beams are absorbed and detected. A cover plate typically is located over the array electrical contact portion to prevent x-ray beams from impinging on electrical conductors outside of the active area of the array. The cover plate typically is secured to the detector array by an adhesive applied between the array active portion and the electrical contact portion.
If the electrical conductors are coated with CsI, such coating can adversely affect image generation. Particularly, the electrical characteristics of the conductors could be impacted by the coating, and the signals obtained from the coated conductors may not accurately represent the characteristics of an attenuated x-ray beam which impinges on the array active portion. In addition, if CsI is applied to the area of the detector array to receive the adhesive, i.e., at the interface between the active portion and the electrical conductors, such CsI can affect the integrity of the bond between the adhesive and the detector array.
In an attempt to apply the CsI coating to only the active portion of the detector array, shadow masks typically are used. The shadow mask is intended to facilitate coating the entire array active portion with CsI while simultaneously preventing any migration of CsI into the inactive portion of the array, i.e., the portion of the array to receive the adhesive and the electrical contact portion.
Shadow masks typically are frame-like members with an inner periphery having substantially the same or slightly larger dimensions as the outer periphery of the array active portion. The frame member covers the array inactive portion.
Prior to coating the active portion of the detector, the shadow mask is positioned over the detector array so that an inner periphery of the frame member is substantially aligned with an outer periphery of the array active portion. The mask covers both the electrical contact portion and the area designated to receive the adhesive, i.e., the array inactive portion. The mask and detector array assembly is then located in an evaporator, and CsI is deposited on the assembly.
Systems presently used provide no positive registration or positioning of the shadow mask on the array, and thus precise location of the mask is highly dependent upon the skill of the operator. Even when using the shadow mask, if the substrate is not precisely located, CsI may be deposited on the inactive portion of the detector array, e.g., the CsI may migrate into the inactive portion. Similarly, misalignment between the shadow mask and the array may result in a section of the detector array active portion not being coated with CsI, which also is undesirable.
It would be desirable to provide methods and apparatus for facilitating the deposition of CsI on only the active portion of a detector array and for preventing deposition of CsI on the array inactive portion. It also would be desirable for such methods and apparatus to be simple to implement and utilize.